Pyroelectric detectors which convert electromagnetic radiation into an electric output signal are known. Such detectors may be used in thermal imaging devices. The detectors may be configured to detect radiation in the infrared region of the spectrum. However, such detectors may have limitations.
For example, one type of pyroelectric detector may comprise a pyroelectric material positioned between two electrodes. If the pyroelectric material is an insulator then a capacitor is formed. Electromagnetic radiation which is incident on the detector may cause an increase in the temperature of the pyroelectric material which will affect the charge distribution within the pyroelectric material. This affects the charges stored on each of the plates of the capacitor and causes an electric pulse to be provided between the two electrodes.
These types of detectors can only be used to detect changes in temperature. The electric pulse is only provided when there is a change in the charge distribution in the pyroelectric material. Therefore in order to be used to detect incident electromagnetic radiation the incoming radiation must be chopped in order to enable a continuous signal output signal to be provided.
Also the temperature increase of the pyroelectric material caused by the incident electromagnetic radiation may be very small. In some examples the temperature increase may be in the region of 0.01 to 0.1° C. This may only create a weak output signal which may then require amplification.
The output signal which is provided by the capacitive detectors is dependent upon the surface area of the detector. Therefore decreasing the size of the detectors decreases the responsiveness of the detector. This makes it difficult to decrease the size of the detectors and makes it difficult to integrate the detectors into other devices.
Also the capacitive detectors do not distinguish between different wavelengths of radiation. The capacitive detectors can provide an output signal which may be dependent upon the intensity of the electromagnetic radiation signal but which provides no information regarding the wavelengths of the radiation within the electromagnetic radiation signal.
It would be useful to provide an apparatus for sensing which overcomes these deficiencies.